rmmchl (is that your name?)
When I picked up my car unrestored in 1999, with the hard top on, my ears popped when the door was closed, a sure indication of a near-airtight seal.
Of course, you have less seal with the soft top up, but it should still be pretty good.
Remember a touchless automatic wash has overlapping 100% coverage of water at about 1100 PSI, generally flowing at about 40 GPM. This is a true test of any seal. Even on conventional sedans you might get some leakage now and then.
My wash serves everything and everybody: I have seen a 1946 Buick go in last week. Despite their rarity in the working class neighborhood where my wash is, I get some Mercedes sedans in there, once in a while an SL500. Corvette convertibles, Camaro T-Tops, etc. Most of them do OK, but nearly all the convertibles do have some leakage. I have not seen it too severe, except for one lady this week with a Camaro convertible--leaked like a sieve.
Our 113's are small enough that they are easy to wash by hand, and given your experience I wouldn't go through any automatic again!
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored